Descending tracts of the lateral columns of the rat spinal cord: a study using the horseradish peroxidase and silver impregnation techniques.

The location of the cells of origin and the projection areas of descending fibre tracts of the spinal cord lateral columns were examined in rats. Unilateral micro-transections of subpopulations of lateral column fibres, at C2 or T10, with subsequent application of horseradish peroxidase to the severed axons, allowed identification, by retrograde labelling, of those cell groups projecting to the spinal cord through the lateral columns. Additionally, the pattern of fibre and preterminal degeneration below the level of transection was examined using the Fink-Heimer silver impregnation technique. The largest number of labelled cells was observed in the ventral portion of nucleus gigantocellularis, projecting ipsilaterally through both the anterolateral (AL) and dorsolateral (DL) columns. Labelled cells were observed in the dorsal portion of the lateral vestibular nucleus (lv) following a T10 transection, and throughout the necleus following a C2 transection. Protein marker was observed in the large Deiters' cells of the lv, ipsilaterally. Also following an AL, but not a DL, column transection, retrograde labelled cells occurred throughout necleus reticularis pontis oralis (rpoo), bilaterally. At the border of rpoo and the lateral lemniscus, a discrete group of labelled cells was observed bilaterally following a DL column transection. This group of reticulospinal cells was located in a position similar to that of the A7 cell group reported in histofluorescence studies. The most extensive group of labelled cells following a DL column transection occurred in the magnocellular portion of the contralateral red nucleus. Although lavelled cells were observed in the red nucleus following either a C2 or T10 DL column transection, labelled cells were more numbeous and extended further rostrally and dorsally, following a high cervical transection. Labelled cells in nucleus raphe magnus were also more numerous following a DL column transection. Additional groups of labelled cells were seen following both an AL or DL column transection. These groups included necleus subcoeruleus ipsilaterally, and nucleus reticularis ventralis and the nucleus of the tract of spinal V, bilaterally. Labelled cells were observed as far forwards as the hypothalamus, occurring predominantly in the paraventricular nucleus, ipsilaterally. A few labelled cells were observed in the lateral hypothalamus. Some cell groups were labelled only after a C2 transection. These included the interstitial nucleus of Cajal, ipsilaterally, the descending vestibular necleus and the deep layers of the superior colliculus, contralaterally, and the central grey matter and nucleus raphe pallidus. Fibre and preterminal degeneration resulting from unilateral AL or DL column transection was examined. Following an AL column transection degeneration was most intense in the ipsilateral laminae V, VI and VII...